[unreadable] Xenotransplantation is of interest due to the insufficient supply of human organs. The pig is considered a likely donor species for humans. However, there are major barriers to successful xenotransplantation. The first two barriers, hyperacute rejection and acute vascular rejection (AVR), are mediated primarily by humoral immunity. If hyperacute rejection is avoided, AVR will occur. Strategies to interfere with AVR include reducing humoral immunity or inducing tolerance in the recipient, and decreasing immunogenicity or inducing protection in the graft. Our goal is to investigate induction of protection in the donor organ from AVR and achieve accommodation. HYPOTHESIS: The cytokines IL-4 and IL-13 induce protection in pig vascular tissues from effectors of immunologic injury, including complement, induction of adhesion molecules, and apoptosis. Activation of specific cellular mechanisms result in protection from xenogeneic injury. SPECIFIC AIMS. I: Characterize the activation mechanism and identify the specific genes that are responsible for protection in endothelial cells activated with IL-4/IL-13. IL-4-mediated phosphatidylinositol-3 kinase (PI-3K) and Akt kinase activation and post-translational modification of the pro-apoptotic protein Bad will be investigated. Selected genes will be tested to determine if they actually mediate protection, using RNA interference to block gene function. Protection by overexpressing the gene after recombinant adenoviral transduction of endothelial cells will also be used. II: Identify other candidate genes potentially involved in cytoprotection induced with IL-4. Highly focussed experiments will be performed using a pig cDNA microarray to identify genes that change expression after IL-4 treatment in the presence and absence of specific PI-3K inhibitors. III. Induction of protection by IL-4 in an artery model of pig-to-primate xenotransplantation. Protection will be induced by incubation of a pig artery with IL-4 and by gene transfer of IL-4, IL-13, or other specific identified genes into the arterial tissues. Protection of the artery from injury that normally occurs upon perfusion with human blood will be assessed. Accomplishing these goals will result in understanding mechanisms of protection in pig tissues and to what extent they contribute to successful xenotransplantation, and would facilitate understanding the pathophysiology of vascular diseases. [unreadable] [unreadable]